This invention relates to a method and machine for automatic focusing in a projection system with continuously variable magnification.
In a process camera or an enlarger for photographing a picture image projected onto a photosensitive material by using a focusing lens, or a projection system such as a projector, or the like, for projecting an enlarged picture image onto a screen, an automatic focusing projection system with continuously variable magnification has been often employed so that a trimming of an original picture may readily be performed and so that it may be observed whether the magnification scale is being increased or reduced when the magnification scale is varied.
In one conventional automatic focusing projection system, while a photosensitive material is fixed, the focusing lens and the original picture are moved together by using cams. In this case, the manufacture of the cams is rather troublesome and thus requires high cost. Further, when the focusing lens is replaced with another one having a different focal distance, different cams are required and it is rather troublesome to adjust the focusing of the new lens.